The present study is designed to determine the patterns and mechanisms of ventricular activation of intra-ventricular conduction disturbances, ventricular tachyarrhythmias and chronic myocardial infarction and correlate these findings with the scaler electrocardiogram (ECG) and vectorcardiogram (VCG). Previous studies in man and animals have suggested that very similar patterns in the ECG or VCG may be produced by several different mechanisms which are identifiable by activation mapping. In this study the sequence of epicardial, intramural and endocardial activation of the ventricles will be determined during cardiac catheterization and/or intrathoracic surgery using unipolar and bipolar electrode recordings. During intra-cardiac surgery unipolar and bipolar electrograms are simultaneously recorded at 40-80 epicardial sites and selected intramural and endocardial sites in addition to ECG leads 1, 2 and 3, and a stable reference ventricular electrogram. Electrograms are recorded from the ventricular specialized conduction system (VSCS) with a probe introduced through an atriotomy or ventriculotomy. From these data, isochronic activation maps are constructed and the continuity of and conduction velocity in certain segments of the VSCS can be determined. These findings are correlated with ECGs and time-normalized VCGs obtained pre- and post-operatively. These techniques will be used to study 1) right bundle branch block, spontaneous, surgically induced, functional (aberrancy), partial or complete; 2) left axis deviation, due to left anterior hemiblock or other causes; 3) left bundle branch block; 4) right and left ventricular hypertrophy; 5) ventricular tachycardia; 6) acute myocardial infarction; and 7) chronic myocardial infarction. The more precise definition and understanding of ECG and VCG patterns obtained by these studies will allow expansion of the clinical utility of the ECG and VCG and more uniform study of the prognosis of various conduction disturbances.